1. Field of the Invention
The present invention relates to a nuclear medical diagnostic equipment and a data acquisition method for a nuclear medical diagnosis wherein radiation emitted from a nuclide (radioisotope: RI) administered to a patient is detected using a gamma (γ) camera, and an RI distribution is imaged on the basis of the detection information.
2. Description of the Related Art
With the technological advancements of hardware and software in recent years, a nuclear medical diagnostic equipment being an equipment for medical use has also made great progress.
The nuclear medical diagnostic equipment includes a measurement unit called “gamma camera”, and it is employed for implementing the nuclear medical examination of a patient. The nuclear medical examination is implemented in such a way that, as stated above, a drug labeled with a radioisotope (hereinbelow, abbreviated to “RI”) is administered into the body of a patient, whereupon an RI distribution within the body is imaged by a gamma camera. The principal techniques of the nuclear medical examination are a planar method (taking the static image of the patient in a fixed direction), and a SPECT method (single photon emission computed tomography: SPECT; taking the tomogram of the patient).
In the case of the nuclear medical examination, a time period of several minutes to several tens minutes is usually expended in acquiring data. Therefore, the data cannot be acquired in the state of one time of breath holding by the patient, over the whole data acquisition time period. That is, the data must be acquired even while the patient is breathing. Accordingly, an acquired image is influenced by bodily motions ascribable to the respiration of the patient. Thus, the image quality of the acquired image, including a positional resolution and a contrast, degrades inevitably.
A technique which acquires data in synchronism with data acquiring phases (respiratory phases) set on a spirogram detected from a patient, in order to reduce or avoid the influence of the bodily motions ascribable to the respiration, has been known as seen from, for example, Kazunori Kan, et al.: “Initial experience of Respiratory-gated lung ventilation/blood flow SPECT examination”, page 590 of proceeding “Nuclear Medicine”, November 2002 (Volume 39, No. 4) issued on Nov. 20, 2002 by the Japanese Society of Nuclear Medicine, and Kazunori Kan, et al.: “Lung ventilation/blood flow SPECT based on Automatic superposition software”, page 590 of proceeding “Nuclear Medicine”, November 2002 (Volume 39, No. 4) issued on Nov. 20, 2002 by the Japanese Society of Nuclear Medicine. In the case of the data acquisition method, when the respiratory phases to be used for the data acquisition are divided more finely, the influence of the bodily motions ascribable to the respiration can be reduced to a considerable degree.
Further, JP-A-2001-346773 discloses a technique in which the respiratory movement of a patient is detected by a respiration detection device, and an imaging device is controlled so as to acquire data in respiratory rest periods of small bodily motions in accordance with the detected respiratory movement.
In the case of the above respiratory-gated data acquisition, however, acquisition counts per finer phase decrease basically, and hence, statistic noise and the like noise become predominant, to pose the problem that the degradation of an image is incurred due to the noise. In a case where the respiratory phases are coarsely divided contrariwise, there is incurred a contradictory situation where the image degradation ascribable to the decrease of the acquisition counts can be relieved, but where the effect of suppressing the influence of the bodily motions ascribable to the respiration decreases.
Further, the respiratory-gated data acquisition is performed using a respiratory gating monitor. In this regard, it is pointed out that the respiratory gating monitor sometimes fails to reliably sense the breathing state of the patient. In such a case where the breathing state cannot be reliably sensed, the extension of the data acquisition time period or the decrease of the acquisition counts is incurred, resulting in a situation where the throughput of the patient lowers or where the image degradation becomes drastic.
Still further, in the case of the respiratory-gated data acquisition, the image is taken under the averaged bodily motion of the patient over the total time of the individual data acquiring respiratory phases. Therefore, the respiratory-gated data acquisition is not a little influenced by the bodily motions ascribable to the respiration, as compared with data acquisition in the non-breathing state of the patient, so that the image quality of the acquired image is unsatisfactory.
Meanwhile, as another problem it is permitted to acquire the data only in the respiratory rest periods of the patient. When an image is generated using only the data acquired in the respiratory rest periods, the degradations of the positional resolution and contrast of the image attributed to the bodily motions of the patient can be suppressed. In this case, however, data are not acquired in the respiratory periods or breathing state of the patient. This poses the problem that the number of samplings decreases to degrade the smoothness, namely, sensitivity of the image.
It is therefore desired to develop a technique for taking an image of higher positional resolution and sensitivity in compliance with clinical purposes.